Service rated Transfer switch 480 V 3 phase.

Two feeds
One from Generator Breaker other from utility transformer (No breaker inbetween).

Both underground directly to transfer switch(service rated) Which has a breaker for Both incoming lines.

Generator feed is three phases plus Ground, Power co. feed I take it MUST be three phases plus Neutral. Even though neuutrals not to be used its required for grounding.
Thus you have an equipment Ground from Generator , AND a neutral from Power Co. Hooking to the same bar.& Neutral bar Must be tied to the case.
Any comments or Input???

Yoopers

Ernie- 3 phase from the generator for that voltage does not have to be grounded but it will have to have an equipment ground. look at 250.20(B). If the neutral conductor of the utility and the equipment grounding conductor are terminated in the transfer switch I think it would be best if the equipment grounding conductor from an ungrounded 480v. supply (generator) is tied to the enclousure of the transfer switch. I further think that the neutral of the utility supply should be tied to a bar in the transfer switch with a Main Bonding Jumper that is removable.

George
If that generator is wye connected wouldn't we be required to bring the neutral to the service disconnecting means and bond it pursuant to 250.24 (B). The reason that I bring that up is it is very common to use one generator to supply several emergency loads of which the fire pump is just one. In such a case the generator will be wye connected in order to supply the emergency lighting loads.
--
Tom Horne

Tom - If it were grounded I would agree with you based on your code reference of 250.24(B). But in the example Ernie cited their was no neutral load and based on the option to ground in 25020(B), he might not bond the wye SDS. If he did bond the system and also the utility Service he probably would end up with a 4-pole transfer switch with each system with it's own Grounding Electrode. (he could also use the same grounding electrode) but he would have to run the grounded conductor through a pole on the transfer switch.
IMHO or as I understand the code.

Both are 277/480 volt Y's thus I said Neutral required on Power Co.Service. Disconnect as its ist in Transfer Sw. But not from Generator as Breaker located at the Generator.

Okay Ernie- Now that I understand what you have ie: 480/277v. for both the generator and the utility, you will need a 4-pole transfer switch to disconnect the SDS grounded conductor from the utility grounded conductor. Each will need a gorunding electrode and without the grounded conductor running through a pole of the transfer switch you'd be grounding your two systems in two places which is a code violation. Your first post only mentioned 480v generator which would lead me to think that the generator was running ungrounded single voltage.

Transfer Switch is Service Rated Fire Pump switch. As its 480 volt 3 Phase I;m sure theres no neutral prefusions at the transfer switch. I;ll check MoNday & see .

Transfer switch 480volt 3 phase service rated
No neutral bar present.

I think if it's single voltage - in other words, ungrounded straight 480v. you only need a 3 pole transfer switch. You will still be bringing an GEC from the generator to the transfer switch to ground the equipment. As I recall there is a need for ground indicator lights but I don't know where I saw that. Also typically ungrounded systems are Delta not Wye. You can check to see if you have any voltage between any of the 3 legs and Ground to find out if it's a grounded system. No insults intended Ernie cause I'm sure you already have done this. Also look in Soares Grounding 8th Ed. p. 43-51 for a brief overview of ungrounded systems and pictures too

George]
The Generators a Y The power Co, Feeds a Y

Both 277/ 480.
Generator Neutrals Grounded at the Gen . Set
Power co. Requires a Neutral per Code Even thought its a 480 3 phase Because a Neutrals present at the transformer.
Thus it HAS to be brought in for Grounding purposes! The Question is Theres a EQuipment Gr. From Generator and a Neutral from Power Co. Service coming into a Transfer switch at the Fire pump set up from Ground only/

Ernie- I think since both supplies are grounded wye's that you are required to have an EGC and the neutral brought to the transfer switch. The neutral will have to be switched by the transfer switch so you don't end up with redundant neutral bonding. As for the EGC - All of this equipment must be tied together via an EGC. I don't know what your Grounding Electrodes are or where they are in relation to your supplies but you will need a GEC running from the utility and the generator to the grounding electrode(s). I've got some engineer diagrams if I can find them I'll post them here. Drawn and published by IEEE.

Generator Feeds transfer Switch off a Breaker. (there are several breakers feeding
other transfer switchs besides Fire Pump). Thus Ist Disconnect Neurtal Must be grounded there (Generator), So from there To Fire Pump transfer Switch only a Ground is required as the Pumps 480 volt 3 phase.
Now the power co. side :
As theres NO disconect switch ahead of the Transfer swith Except the one on the Service rated Transfer switch The Neutral Must be brought in and grounded here. (The fire Pump transfer switch is a 3 pole only .

It appears that the load on the transfer switch needs a neutral - Where will it get a neutral when the utility is disconnected from the load?

If you don't need the neutral then just bring in the EGC and use a 3 pole sw.

[This message has been edited by George Little (edited 09-27-2006).]

I believe 250.30(A)(1) Exception 1 allows bonding neutrals from separately derived systems, and I can see no reason it wouldn't apply in this instance. I don't see a problem with bonding the neutrals.

[This message has been edited by SteveFehr (edited 09-28-2006).]

Steve- If you Bond the utility supply with the Main Bonding Jumper at the Service would you approve of installing a jumper wire between the neutral screw of a receptacle and the ground screw of the receptacle somplace else downstream on the system? That's essentially what you would have if you bond at the Utility Service and then remotely at a generator an don't switch the neutral with the transfer switch. The concern is having current flow on the grounding conductor. If a person is not using the Grounded conductor for a current carring conductor then I agree with you. Code reference: 250.28, 250.142 NEC '02 Ed.

Edited to add code reference.



[This message has been edited by George Little (edited 09-28-2006).]

George, I'm aware of the implications of bonding the neutral to ground at multiple points, but it IS legal by NEC in the specific case of multiple derived sources, and absolutely required for make-before-break connections like UPS maintanance bypass switches and paralleling/load-sharing generators where switching the neutral is impossible.

Thus, it is allowed by NEC 250.30(A)(1) in instances like this because there is no way around it. 250.30(A) allows exceptions to this in several other instances, too. Edit- my mistake, I said this was unchanged from 2002, but 250.30(A) is annotated as changed in NEC 2005.

[This message has been edited by SteveFehr (edited 09-28-2006).]

Steve.... I'm still not sure of the actual theory behind your statement (regarding make / break and UPS)...but I'm a believer!!

I got confused on this point, installed a UPS incorrectly, tha customer went to test the system..... and I got to spend $$$$ replacing all the stuff my incorrect neutral connection fried. OOPS!

renosteinke, I work in an industry where power interruption in not acceptable. We have redundant utility feeders, redundant generators and redundant UPS systems, most of which are designed for make-before-break switchover, with few exceptions. The equipment has to be designed to parallel and always includes circuitry to ensure phase-matching and open the breakers if paralleling is lost. It's especially important on UPS systems where the UPS, Static Switch and Maint Bypass switch are fed from 2 or 3 separate sources.

It certainly puts a burden on the contractor to test properly and do it right the first time, especially in situations when we're unable to schedule an outage or test offline and have to test on the operational building. But, that's why we're paid the big bucks!

As this has changed from 2002, I'll transcribe:
NEC 2005, 250.30(A)(1) Exception 1: For separately derived systems that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each power source shall be permitted.

That's a mouthful, but if you break it down, it pretty clearly authorizes bonding the neutrals together. It's stated elsewhere in 250 that the neutral bus bar is considered a bonding jumper.

Same clause, with extraneous verbage removed for clarity:
For separately derived systems that are dual fed in a common enclosure, a single system bonding jumper to the grounded circuit conductors from each power source shall be permitted.

[This message has been edited by SteveFehr (edited 09-28-2006).]

Steve thanks for your comments and insight. I agree with you entirely (Don't tell anyone I agreed with an engineer) and have seen the article in IEEE magizine March 2001 that explains it very well including the first make/last break concept. Good to banter with someone who has done his homework.

Upon closer inspection, I think I was reading it slightly wrong- it allows tying the neutrals of the two services together, but only if the two neutral systems are bonded to ground ONLY at that tie point. Thus preventing the ground wires carrying and neutral current.

So, Yoopers must bond the generator neutral and panel neutral to the utility neutral and ground at the transfer switch and not to ground anywhere else.

I concur.

Guys
Sounds good but can't be done. Why As I Stated before '
#1 Generator has Several breakers at it one feeds Fire Pump Transfer Switch other feeds 4 pole to Bld loads. SO Generator MUST be bonded at ist Breaker.
#2
Fire Pump transfer switch is Fed from the NORMAL power source straight from the transformer THUS MUST be bonded at ist disconect(Transfer switch).
So again Three Phases and a Equipment Gr. comes from Generator is Right.
So in Firepump transfer switch you have From Generator 3 phases and Equipment gr.
From Service 3 phases and Neutral. I feel there NO Way with this set up it can be hooked up to code the way its set up.

So Yooper- Your back to a 4-pole transfer switch.

Except all units are IN PLACE . Fire Pump 3 pole Transfer switch.Its at a Casino Soooooooooooo .

How are the neutrals handled in the other transfer switches? I don't see a problem with parallel neutral & ground current depending on what other services the transformer is feeding and how the neutrals are handled in those transfer switches. Wouldn't you be okay if the other transfer switches were all 4-pole or had no neutral either? That way neutral current wouldn't find a return path back to the transformer neutral if it ventured up the equipment ground back to the generator because that neutral is isolated. If that generator neutral has a permanent bond to the transformer neutral elsewhere, then you've got a problem.

[This message has been edited by Jps1006 (edited 09-30-2006).]

Yoopersup, why *must* you bond the neutral at the generator? So long as you're not switching the neutral at the breaker, exception 1 would allow you to bond the neutral at the transfer switch instead of the generator & the neutral bus would still be contiguous and feed the other circuits, and no multiple grounds. It's legal and electrically sound.

Electrically, it really doesn't matter where the neutral is bonded, just so long as it's electrically contiguous. Sure, it's best to ground it at the source, but it doesn't have to be.

Unless there are other complications in the design we're not aware of/taking into account?

[This message has been edited by SteveFehr (edited 10-01-2006).]

Steve's correct, 250.30(A)(1) says you can bond a SDS any place from the source to the first disconnecting means, '02 NEC

Look back at Posts . The ist Breaker Is on the Generator! In fact there two Breakers there (ONE feeds Fire pump transfer switch) Break (Second feeds another Building 4 pole transfer switch).There more then one transfer switch involved here.

So if your first disconnect/breaker is at the generator, and we have established that you are running a grounded SDS you are required to install your MBJ at the generator and you will be running 4 conductors to your transfer switch. The equipment ground will be just that and the neutral will be terminated on one of the 4 poles of the transfer switch.

Again Fire Pump transfer Switch Alreay in Place is 3 pole. And Remember you also have a SERVICE coming from another Transformer to the Fire Pump Skid THUS.
Generator Hot Hot hot Ground
Power Co. Hot Hot Hot Neutral
Again FP tranfer switch 3 Pole in Place .
There really NO place for a Neutral in the fire Pump transfer fer Sw. Just Ground Connections. Service pipe comes out of the concrete directly in FP Skid.
Thus 3 phases and Gr. one side Three phase and Neutral other side.

Ah, there is only one neutral, I thought you were bring the neutral from the generator, too. And it's not even being used, correct?

If the neutral is not used, the neutral terminal should either be grounded at the transformer or floated with no lugs whatsoever; no sense wasting copper running a white wire to nowhere.

If it's already in place, color it green and call it a ground If there's no neutral current and you're just running it from a grounded T0 to the ground bar in the transfer switch, it's not a neutral,

[This message has been edited by SteveFehr (edited 10-01-2006).]

Steve I know what you are saying and I agree with you if he does not need a neutral for his load.

Your Getting Close , What about the Neutral Required to go to the ist disconnect Switch(From Power Co. transformer To Fire Pump Breaker.) Call that a Ground too??

Well- I don't remember where your overcurrent protection is and if it's part of your transfer switch or next to it, then the Grounded and Grounding conductor are one and the same coming from your utility company. So your Neutral may well also be your ground.

Yoopersup
I started out in electrical work as a laborer with a power production crew in the Air Force. This issue was the one that always caused the most discussion. The practice that developed out of necessity was to not bond the neutral at the generator because it did not transfer at the switch. If the neutral does not transfer at the other transfer switch then the generator is not in fact a separately derived system because it's neutral is bonded to ground and to the power companies neutral at that other transfer switch. If it is not an SDS it should not have been bonded at the generator.

Leaving the code alone for the moment what you don't want is any neutral current using the EGCs as a normal current path even under a single failure scenario. What you have now is a neutral from the generator running to the other emergency panel and an equipment grounding conductor or EGC running to the fire pump transfer switch. Bonding the neutral of a non SDS generator to the frame was the error we had to get corrected on almost every generator set prior to acceptance. The project managers never buy anything that is not specified or required at inspection. As a result they never buy the neutral isolation kit from the generator manufacturer and they never order the forth pole in the transfer switch. Since the generators are shipped with bonded neutrals the installers leave them that way because they don't have the neutral isolation kit on hand and it is a rare heavy industry crew that will have someone that will spot the error.

I have installed both SDS systems and common neutral systems from Uganda to french frigate shoals and from the Argentine pampas to Alaska. As long as I kept clear in the documentation and in my head whether or not the system in question was a separately derived system I always got acceptance and passed inspection. That many engineers and electrical inspectors can’t all be wrong. All you need to do is isolate the neutral of the generator from the frame and leave that common neutrals only bonding point at the other transfer switch alone. The only concern that leaves me with is I cannot trace a low impedance fault current path from the case of the fire pump motor back to the neutral of the generator in order to clear a fault under generator operation of the fire pump. What may be true is no such fault clearing path is wanted because fire pumps should run to destruction rather than fail to pump the fire protection water that is the whole reason for their existence. I just get concerned that this mite leave a hazard to personnel. What mitigates against that is the fact that the fire protection piping is very likely to be a large metallic system that includes underground piping that will have been used as a grounding electrode for the buildings utility supplied service the neutral of which is common to the generators neutral. Even though that mite well work as a fault clearing path I’d much rather have the fault clearing pathway be electrician built and maintained.
--
Tom Horne

"This alternating current stuf is just a fad. It is much too dangerous for general use." Thomas Alva Edison

[This message has been edited by tdhorne (edited 10-04-2006).]

Still back to Ground from Generator
Neutral from Power Co. Transformer
Neutrals required to be bonded
Ground from generators suppose to be kept seperate from neutral yet bonded to case.

"Still back to Ground from Generator
Neutral from Power Co. Transformer
Neutrals required to be bonded
Ground from generators suppose to be kept seperate from neutral yet bonded to case."

If the generator is properly wired with the neutral isolated form ground then that grounding conductor is bonding the frame of the generator to the common bonding point of both sources of power.
--
Tom Horne